While the top ten favourite books of children at primary school are dominated by J.K.Rowlingâs Harry Potter series, by the time children have reached secondary school the top slots are occupied by the vlogger Zoella’s novels.

Keith Topping, a professor of educational and social research at the University of Dundee, who was commission by Renaissance Learning to conduct the research, said: âAlas, the Zoella books are not as challenging as the J.K. Rowling books, we do have an issue there.

âI do grieve about children wanting to read books that are not challenging enough.”

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J.R.R Tolkienâs The Hobbit has been a constant feature on the favourites list previously, but it has âdisappearedâ in recent years, according to Prof Topping.

He added: “The decline in children’s reading age during secondary school is pronounced.In previous years there was some evidence of it but this year is much more striking.”

The research, which surveyed the reading habits of over 800,000 children in the UK, found that children leave primary school with the correct reading age. However, by the time they sit GCSEs at age 16, their reading age is that of a 13-year-old. Â